switchMap, mergeMap

const switchBtnEl = document.getElementById('switchBtn');
const switchBtn$ = Rx.Observable.fromEvent(switchBtnEl, 'click');
const mergeEl = document.getElementById('mergeBtn');
const mergeBtn$ = Rx.Observable.fromEvent(mergeEl, 'click');


const goFetchFn = () => {
  return Rx.Observable.fromPromise(
    fetch('http://localhost:3000/gogo').then(res => {
      console.log('goFetchFn');
      return res.json();
    })
  );
}

const comeFetchFn = () => {
  return Rx.Observable.fromPromise(
    fetch('http://localhost:3000/come').then(res => {
      console.log('comeFetchFn')
      return res.json();
    })
  );
}


const clickSwitchGo$ = switchBtn$.switchMap(() => {
  console.log('click!! switch~~');
  return goFetchFn();
});


const clickMergeCome$ = mergeBtn$.mergeMap(() => {
  console.log('click!! merge~~');
  return comeFetchFn();
})


clickSwitchGo$.subscribe(data => {
  console.log('subscribe switch!!', data);
});

clickMergeCome$.subscribe(data => {
  console.log('subscribe merge!!', data);
})